Kimchi is the traditional Korean fermented vegetable food which has been an important element for the diet and nutrition for Koreans and has been acknowledged world-widely. The main vegetables for Kimchi are Korean cabbage and radish, to which garlic, ginger and hot pepper powder are added as spices and condiments and salts are added for salt-fermentation. Among many kinds of Kimchi, cabbage Kimchi is the most dominant, taking 70% of Kimchi intake. The Korean cabbage, the one major vegetable for Kimchi, contains sugar and lactobacilli which ferment the sugar included in the vegetables and spices and condiments to generate taste components such as organic acids including lactic acid and acetic acid, carbon dioxide and alcohol and functional components such as β-sitosterol, glucose inolate, isothiocyanate and capsaicin.
The long-term storage of Kimchi is limited because some time after ripening rancid microorganisms are growing in Kimchi to cause acidification, gas generation and tissue softening. Therefore, a special technique to prolong the storage time is required to increase the utility of Kimchi as an excellent fermented food.
The conventional methods for long-term storage of Kimchi are exemplified by refrigeration, freezing, heat sterilization, antiseptic treatment, the combination of antiseptic treatment, refrigeration and heat sterilization, high-salt treatment, applying a pH regulator, etc. However, these methods have problems of reducing quality and economic efficiency.
‘Food irradiation’ is to irradiate energy, such as gamma ray (Co-60 or Se-137), electron beam or X-ray, generated from radioactive materials or from a radioactive ray generator, to food at the level of 0.01 kGy˜50 kGy for the purpose of germination inhibition, ripe extension, extermination of parasites and vermin, prevention of decomposition and sterilization of pathogenic microorganisms in food. A chemical fumigation agent such as ethyleneoxide has been used for sterilization of food and household goods, which is, though, lethal to human and destroys environment. Thus, most of advanced countries have been used food irradiation which is efficient and not harmful for human.
After studying on the method for gamma ray irradiation to increase the shelf stability of Kimchi based on the advantages of irradiation, Cha et al reported that the storage time of Kimchi at 10° C. was more than double when Kimchi was irradiated with low dose of gamma ray at the level of 2˜3 kGy (Cha B S et al., Korea J. Food Sci. Technol. 21: 109-119, 1989). Kang et al also reported that when Kimchi was irradiated with gamma ray at the level of 3 kGy and then stored at 5° C., the storage time was extended more than two months, compared with when Kimchi was not irradiated before storage (Kang S S et al., Korea J. Food Hygiene. 3: 225-232, 1988). The proposed methods above are all using low dose of irradiation at the level of 5 kGy or less. However, to preserve Kimchi under the severe environment such as desert or space, complete sterilization is required and accordingly high dose of irradiation or high temperature treatment is required. However, over-irradiation or excessive heat-treatment on Kimchi results in the decrease of physical property, decolorization and development of other tastes and smells, drawing a limitation in industrialization of Kimchi.
The present inventors packed Kimchi with nitrogen charging in the ripening stage and treated the packed Kimchi with heat. Then, the Kimchi was quick-frozen, followed by irradiation. As a result, the present inventors completed this invention by confirming that the sensory quality of Kimchi was not reduced by heat and irradiation and the long-term shelf stability was prolonged even under the severe environment.